Supplemental Oil and Gas Disclosures (Unaudited) (Details 2)	12 Months Ended
	Dec. 31, 2011 MBbls	Dec. 31, 2010 MBbls	Dec. 31, 2009 MBbls	Dec. 31, 2008 MBbls
Oil Reserves (MBbls) [Member]
Reserve Quantities [Line Items]
Proved developed reserves	95,000	5,760,000	5,502,000	4,365,000
Proved undeveloped reserves	107,000	1,012,000	1,367,000	1,433,000
Total proved reserves at period end	202,000	6,772,000	6,869,000
Reserve Quantity Rollforward
Total proved reserves, beginning balance	6,772,000	6,869,000	5,798,000
Revisions of previous estimates	(88,000)	266,000	1,805,000
Production	(612,000)	(1,360,000)	(1,219,000)
Extensions and discoveries	0	712,000	564,000
Purchases of reserves in place	0	293,000	0
Sales of reserves in place	(5,870,000)	(8,000)	(79,000)
Total proved reserves at period end	202,000	6,772,000	6,869,000
NGL (MBbls) [Member]
Reserve Quantities [Line Items]
Proved developed reserves	40,000	415,000	188,000	139,000
Proved undeveloped reserves	60,000	74,000	16,000	0
Total proved reserves at period end	100,000	489,000	204,000
Reserve Quantity Rollforward
Total proved reserves, beginning balance	489,000	204,000	139,000
Revisions of previous estimates	22,000	310,000	166,000
Production	(88,000)	(132,000)	(106,000)
Extensions and discoveries	0	107,000	5,000
Purchases of reserves in place	0	0	0
Sales of reserves in place	(323,000)	0	0
Total proved reserves at period end	100,000	489,000	204,000
Gas (MMcf) [Member]
Reserve Quantities [Line Items]
Proved developed reserves	676,000,000	24,795,000,000	32,387,000,000	40,988,000,000
Proved undeveloped reserves	480,000,000	790,000,000	1,124,000,000	1,024,000,000
Total proved reserves at period end	1,156,000,000	25,585,000,000	33,511,000,000
Reserve Quantity Rollforward
Total proved reserves, beginning balance	25,585,000,000	33,511,000,000	42,012,000,000
Revisions of previous estimates	(1,903,000,000)	(6,303,000,000)	(623,000,000)
Production	(3,322,000,000)	(7,065,000,000)	(10,449,000,000)
Extensions and discoveries	0	4,749,000,000	3,365,000,000
Purchases of reserves in place	0	876,000,000	0
Sales of reserves in place	(19,204,000,000)	(183,000,000)	(794,000,000)
Total proved reserves at period end	1,156,000,000	25,585,000,000	33,511,000,000